Question

146

What happens if I don't pass a parameter in a Javascript function?

rated 0 times [ 148] [ 2] / answers: 1 / hits: 101370 / 12 Years ago, tue, june 19, 2012, 12:00:00

I am new to the world of Javascript and am tinkering with writing very basic functions and stumbled upon the example below by accident and am unsure why it works when I am not passing a parameter when the function demands it.

Sample function

function myfunction(x) {

    alert(This is a sample alert);

}

Now if I call the function myfunction(); I am presented with the alert. Why is that that I am able to call the function without any errors or warnings when I have not passed a parameter?

EDIT

I did not expect so many great answers and I am by no means in a position yet able to say which answer is the best so am I able to request people to suggest the best answer and I'll award the acceptance to that person.

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darleneh

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3 Years ago

answered 12 Years ago katianatasham · Accepted Answer

Nothing will happen- meaning you won't get an error or a warning as passing the parameters in javascript is optional.

All the parameters that weren't supplied will have the undefined value.

function foo(x, y, z){

    //...

}



foo(1);

Inside the foo function now:

function foo(x, y, z){

    x === 1

    y === undefined

    z === undefined

}

You can even pass more arguments, like:

foo(1,2,3,4,5,7); // Valid!

You can know the amounts of parameters supplied by arguments.length from inside the function.

function foo(x, y, z) {

    console.log('x value: ' + x);

    console.log('y value: ' + y);

    console.log('z value: ' + z);

    console.log('Arguments length: ' + arguments.length);

}

console.log('Zero parameters');

foo();

console.log('Four parameters');

foo(1, 2, 3, 4);

Example of useful function that handle any amount of parameters:

function max() {

    var maxValue = arguments[0];

    for (var i = 1; i < arguments.length; i++) {

        if (maxValue < arguments[i]) {

            maxValue = arguments[i];

        }

    }

    return maxValue;

}



alert(max(1, 5, 7, 2, 88, 32, 44));